Titanic - Official Trailer2:15

Who could have played Jack and Rose instead of Leonardo DiCaprio and Kate Winslet?Source:Supplied

WE ALL know that the Titanic sank - but do you know who almost played Jack instead of Leonardo DiCaprio in the blockbuster movie?

Do you know which star reportedly had pneumonia during filming and do you know who actually sketched Kate Winslet in the nude?

James Cameron’s 1997 epic turns 20 this year, and two decades on from its record-breaking run at the box office, here are a few little-known facts about the film:

Director James Cameron with Kate Winslet and Leonardo DiCaprio during filming.Source:News Limited

Who turned it down?: Rumour has it that Matthew McConaughey and Gwyneth Paltrow were initially approached to play Jack and Rose but decided to turn it down. When asked about the rumour by MTV, director James Cameron was coy.

“I will neither confirm nor deny,” he said.

“I just don’t think that’s cool to talk about actors that either chose not to do it, or were unavailable, or stupidly decided that there wasn’t enough meat on the bone of the character, or whatever it was.”

Ouch, sounds like someone holds a grudge.

“They should’ve come whimpering back afterwards and said, ‘I will never second guess you again as long as I live.’ But it’s too late. You got one chance, that’s it. And you might want to think about this next time when you get called.”

Fact: This scene had to be shot in one take because it ruined all of the furniture.Source:News Corp Australia

Freezing: When Rose is seen shivering in the icy water after the Titanic has sunk, that’s not great acting by Kate Winslet, it’s genuine.

“I am completely freezing,” wrote Winslet in a diary she kept while filming.

“My dresser has been bugging me to wear a wetsuit, but I can’t. I’d be too aware of it and anyway, my dress is too thin for it.

“Jim (James Cameron) doesn’t want see-through and says this isn’t a wet T-shirt competition, but he does want the dress to cling to me when I’m wet and we’ve done all sorts of camera tests for that. It is so cold, but ... it means my reactions are real, I hope!”

There’s a rumour that Winslet’s decision to ditch the wetsuit resulted in her getting pneumonia.

Leo didn’t actually do the sketch himself. Shock!Source:Supplied

THAT drawing: One of the most memorable scenes in the movie (for teenage boys at least), is when Rose poses nude and Jack sketches her. If you watched the film and thought to yourself, “Wow, that DiCaprio fella can really draw!” well guess what, it wasn’t Leo doing the drawing. It was actually director James Cameron who was the man behind the pencil.

Fun fact: In 2011 the sketch was sold at auction for more than $20,000.

Could Jack have jumped up on the raft too?Source:Supplied

The raft debate: Was there enough room for Jack to climb aboard the raft with Rose and save himself from the deadly water? It’s been a topic of debate for years on the internet, but according to director James Cameron, sufficient room was never the issue.

“Jack puts Rose on the raft, then he gets on the raft - He’s not an idiot; he doesn’t want to die - and then the raft sinks. So it’s clear that there’s really only enough buoyancy available for one person.

“If he got on with her they’d both be half in and half out of the water, and they would have both died. So, he makes a decision to let her be that person.

Leonardo DiCaprio looked pretty chuffed with himself at the film’s premiere.Source:Getty Images

Poisoned chowder: During filming, 80 crew members were violently ill and many were rushed to hospital when someone spiked a pot of lobster chowder with an illicit hallucinogen drug called Angel Dust. Leo, Kate and that grandma (Gloria Stuart) didn’t eat any of the chowder.

Extras: James Cameron wanted the film’s 150 main extras to behave exactly like people did back in 1912 so he hired an etiquette specialist to coach them all. A short film called A Time Traveller’s Guide was made which taught the extras how to walk and eat properly. It was played on loop in the wardrobe room.

If only they knew what was coming up ... ICEBERG!Source:Supplied

Dodgy sky: Neil deGrasse Tyson wasn’t impressed with a scene showing the night sky when he watched Titanic for the first time.“It was the wrong sky,” he explained in 2011, “Worst than that ... the left half of the sky was a mirror reflection of the right half of the sky. It wasn’t just wrong, it was lazy.”Tyson wrote Cameron a letter informing him of the mistake but never heard back.More than eight years later he came face-to-face with the director and asked why he never responded and if he was at all concerned about the fact his sky in the film is dodgy.Cameron’s response was sassy.“He answered, ‘Well, last I checked, Titanic worldwide has grossed $US1.3 billion. Imagine how much more it would have grossed had I got the sky correct.”Boom!However, the story had a happy ending for Tyson.Two months after his encounter with Cameron, he received a phone call from the director’s production studios asking for his help to correct the sky for the movie’s 10-year anniversary director’s cut DVD.

Alternate ending: A second ending to the movie was filmed, and no, not one where the Titanic doesn’t sink. In the alternate version, Brock Lovett (played by Bill Paxton), spots Rose dropping the necklace into the ocean and rushes over to confront her and convince her not to do it. But the old lady does it anyway, much to the shock and disappointment of the crew.